Method of making an electron discharge device grid having enhanced thermal conductivity and reduced secondary emission characteristics

ABSTRACT

Thermal conductivity is increased and secondary emission reduced by plating a preliminarily formed grid with copper and then overplating with gold or silver.

United States Patent Inventor Donald R. Kerstetter Emporium, Pa.

App1.No. 31,139

Filed Apr. 23, 1970 Patented Jan. 4, 1972 Assignee Sylvania Electric Products, Inc.

METHOD OF MAKING AN ELECTRON DISCHARGE DEVICE GRID HAVING ENHANCED THERMAL CONDUCTIVITY AND REDUCED SECONDARY EMISSION CHARACTERISTICS 6 Claims, 2 Drawing Figs.

US. Cl 204/16, 204/24, 313/311, 313/348, 313/350 Int. Cl C23b 7/00, C23b 5/48 Field of Search 204/16, 24;

Primary Examiner-John H. Mack Assistant Examiner-T. Tufariello AttorneysNorman J. OMalley, Donald R. Castle and William H. McNeill ABSTRACT: Thermal conductivity is increased and secondary emission reduced by plating a preliminarily formed grid with copper and then overplating with gold or silver.

FORM PRELIMINARY GRID PLATE PRELIMINARY GRID WITH FIRST MATERIAL PLATE GRID WITH SECOND MATERIAL mammal: 4m 3632.485

FORM PRELIMINARY GRID PLATE PRELIMINARY GRID WITH FIRST MATERIAL PLATE GRID WITH SECOND MATERIAL INVENTOR. DONALD R. KERSTETTER ATTORNEY METHOD OF MAKING AN ELECTRON DISCHARGE DEVICE GRID HAVING ENHANCED THERMAL CONDUCTIVITY AND REDUCED SECONDARY EMISSION CHARACTERISTICS BACKGROUND OF THE INVENTION This invention relates to wire grids for electron discharge devices and more particularly to grids having increased thermal conductivity and reduced secondary emission and to a method of making the same.

Grid emission has long been one of the most prevalent forms of electron discharge device failure. This condition; i.e., where the grid begins to emit electrons, causes the device to go out of control thus destroying the operating parameters thereof and making it impossible for the device to perform the job for which it was intended. The grid emission can be caused by a variety of reasons; however, the most common causes are the result of the deposition thereon of barium or barium oxide which has sublimed from the cathode in combination with a relatively high operating temperature of the lateral wire as the result of thermal radiation from the cathode and anode.

Many attempts have been made to control the unwanted grid emission. One of these has been to plate the grid with gold or silver. These materials have a very high work function and alloy readily with the barium from the cathode, thus inactivating the emission-producing substance on the lateral wire. However, this technique does little to help the thermal conductivity of the grid since, while silver has a relatively high thermal conductivity, the amount applied is insufficient to be of much help. Another means utilized has been to try and control the evolution of barium from the cathode. This has taken several forms; such for example, as reducing the operating temperature of the cathode; employing a less active cathode alloy; or employing a less active cathode coating. While all of these techniques are more or less successful, they too change the operating characteristics and require a new tube design to perform the required function.

A third method used has been to try and reduce the operating temperature of the lateral wire directly adjacent the cathode where most of the grid emission occurs. In this regard, of course, the thermal conductivity of the lateral wire is very important since materials having a relatively high thermal conductivity generally result in lower grid emission. Unfortunately however, these materials, such for example, as copper, aluminum and silver, are not sufiiciently strong to make a satisfactory grid lateral wire. Attempts to plate a lateral wire, which is generally molybdenum, tungsten or nickel, with a heavy plating of copper (say 20 percent) have produced a material which is not workable from the standpoint of grid winding.

OBJECTS AND SUMMARY OF THE INVENTION It is therefore, an object of this invention to obviate the disadvantages of the prior art.

It is another object of the invention to enhance the thermal conductivity of electron tube grids.

It is a further object of the invention to reduce the amount of primary or secondary emission from such grids.

Yet another object is the provision of a method for simply and economically manufacturing such a grid.

These objects are accomplished in one aspect of the invention by the provision of a method of manufacturing an electron discharge device grid which has spaced apart siderods and lateral wires stretched thereacross, the siderods and lateral wires to have a given cross-sectional area when completed. As a first step in the operation, a conventional grid is wound using lateral wire and siderods having a smaller cross-sectional area than the given areas of the finished product. This preliminary grid is then immersed in an electroplating bath and plated with a material having a higher thermal conductivity than the grid wire; for example, copper.

The amount of plated material applied is approximately sufficient to bring the cross-sectional area of the lateral wire up to the predetermined size. Thereafter, the plated grid can be overplated with a noble metal such as silver or gold.

The grid provided by this method has excellent thermal conductivity properties, not only in the grid lateral wires but between the lateral wires and the siderods. Mechanical strength is also enhanced because the plating operation securely binds, with an excellent thermally conductive bond, the grid lateral wire to the siderod.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. I is a partial view of a grid made thereby and including a detailed blowup of the lateral wire to grid bonding; and

FIG. 2 is a flow diagram illustrating the method of the invention.

DESCRIPTION OF THE PREFERRED EMBODIMENTS For a better understanding of the present invention, together with other and further objects, advantages and capabilities thereof, reference is made to the following disclosure and appended claims in connection with the above-described drawings.

Referring now to the drawings with greater particularity, there is shown in FIG. I a fragmentary portion of a grid 10 having spaced apart siderods l2 and 14 which can be of any conventional siderod material such as nickel, steel, copper plated steel, etc., and a helix of electrically conductive lateral wire 16 having a given thermal conductivity wound thereabout. Each turn of lateral wire is layed in a notch 18 formed in the siderods and at least the first turn of wire and the last turn of wire have the notch peened over to maintain the lateral wire in position. The lateral wire can be molybdenum, nickel or tungsten or various alloys thereof or other conventionally used materials.

A first layer of material 20 overlies the siderods and lateral wire core 21 and can be, for example, copper. The copper has a higher thermal conductivity than the lateral wire and can be applied by electroplating or diffusion vaporizing techniques. The copper material fills in the notches 18 as shown in the en larged sectional portion of FIG. 1 and effectively increases both the thennal conductivity of the lateral wire itself and also the thermal conductivity between the lateral wire and the siderod. This increase greatly reduces the operating temperature of the grid and thus reduces the primary or secondary emission characteristics.

A second material 22 overlies the first material and is chosen so as to possess a relatively high work function. Materials such as gold and silver are ideally suited to this purpose, and in addition, have the capability of alloying with evolved barium from the cathode and inactivating it as an electron-emitting component. A grid of this construction thus effectively reduces primary emission by virtue of increased thermal conductivity and the overlying coating of material having a high work function.

The unique grid of this invention is fabricated by a new and different method to achieve the aforementioned desirable results. The methods comprises first determining the desired lateral wire size or diameter necessary to achieve the operating characteristics wanted in the tube the grid will be used in. Then a preliminary grid is wound with lateral wire and siderods smaller than those desired in the finished product. After the winding of the preliminary grid, it is cleaned and degreased by conventional operations and then coated up to substantially its final size with a layer of a first material, such as copper. While several coating techniques can be utilized to achieve the result, a preferred method is by electroplating. By plating the entire grid, the copper coating covers evenly the lateral wire and the siderods and penetrates the notches 18 to form a unique thermally conductive bond between the lateral wire and the siderods.

After the first coating is applied, which coating by this technique can be as much as 20 percent of the thickness of the lateral wire, a second coating is applied. The second coating is that of a material having a relatively high work function, such as gold or silver, and this material also can be applied by electroplating. The second layer is much thinner than the first and is generally in the neighborhood of several microns thick, as is conventional.

Thus, there has been provided by this invention a new and novel grid having increased thermal conductivity and consequently reduced primary and secondary emission. The method for providing this grid is also new and provides an easy way of providing a relatively high thermally conductive coating that was not before achievable in a mass production system.

While there have been shown and described what are at present considered the preferred embodiments of the invention, it will be obvious to those skilled in the art that various changes and modifications may be made therein without departing from the scope of the invention as defined by the appended claims.

I claim:

1. In a method of manufacturing an electron discharge device grid having spaced apart siderods and grid lateral wires stretched thereacross, said siderods and lateral wires having a predetermined cross-sectional area, the steps comprising: forming a preliminary grid from siderods and lateral wire of smaller area than said predetermined area, said lateral wire having a given thermal conductivity; immersing said preliminary grid in an electroplating bath and plating thereon a layer of a first material having a thermal conductivity greater then said given thermal conductivity until said cross-sectional area of said siderods and lateral wires is substantially equal to said predetermined size.

2. The invention of claim 1 wherein said grid is subsequently electroplated with a second layer of a material selected from the group consisting of silver and gold.

3. The invention of claim 1 wherein said first plated material is copper.

4. The invention of claim 2 wherein said first plated material is copper.

5. The invention of claim 4 wherein said grid lateral wire is selected from the group consisting of molybdenum, nickel and tungsten and alloys thereof.

6. The invention of claim 5 wherein said copper plating is in the amount of about 20 percent of said lateral wire. 

2. The invention of claim 1 wherein said grid is subsequently electroplated with a second layer of a material selected from the group consisting of silver and gold.
 3. The invention of claim 1 wherein said first plated material is copper.
 4. The invention of claim 2 wherein said first plated material is copper.
 5. The invention of claim 4 wherein said grid lateral wire is selected from the group consisting of molybdenum, nickel and tungsten and alloys thereof.
 6. The invention of claim 5 wherein said copper plating is in the amount of about 20 percent of said lateral wire. 